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Unexplainable Cyclical Lag

Last response: in Networking
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June 8, 2010 9:55:37 PM

Hi everybody. My family and I have been experiencing a real frustrating problem with lag on our wired network and we cannot figure out the rhyme or reason for it.

We have had connection problems in terms of the internet dropping out requiring a router reboot at random times of day for many months now. When it got so bad (6+ times a day) we bought a new router thinking our SMC Barricade was dying (4+ years old). We replaced it initially with a Linksys E2000 only to realize it couldn't handle two Xbox 360's on Live and exchanged it for a Netgear WNR3500L.

While the router fixed numerous connectivity issues (bad NAT/firewall, random internet drop outs), it seemed to leave in its wake a baffling problem of cyclic lag spikes. By cyclic I mean about every minute or so we receive lag spikes of 500-1200ms which lasts about 20-30 seconds persistently after which network latency is restored to ~30ms. Then another minute passes of 30ms normality before the cycle repeats and we spike again. I've graphed the pattern of cyclic lag on a program called PingPlotter pinging www.google.com every 5 seconds for an hour at a time, as well as my ISP's website www.optonline.net. There are peaks and valleys (mountains and valleys more like it) representing what I've described. Note that all networked devices (including especially the Xbox 360's, experience this lag concurrently).

We've had our cable company send technicians out now three times (today being the third time) but to no avail, this problem persists. The technician today replaced our entire cable modem (and gave us an upgrade) and cable connections in our garage where our network equipment resides. They don't seem to detect any problems after their work is done and leave only for me to come home and it still be there.

To better describe how our network is laid out since it is very complicated, I will attempt to 'draw' a diagram and perhaps that can help shed light on potential problem causers.

[Main line cable feed from under street]-----to our house----> (Split into two dedicated lines: 1 for cable TV, the other for cable internet) ---> Cable internet feed to back of [Motorola Surfboard Cable Modem -- brand new today] ------> WAN RJ45 from modem to WAN port of [NETGEAR WNR3500L - brand new router] -----> LAN 1 RJ45 feeds to adjacent [SMC network switch #1], LAN 2 RJ45 feeds to adjacent [SMC network switch #2] ----> Switches #1 and #2 permit LAN connections to split off into what becomes individual RJ45 network drops in each room in our house.

The wiring was done during renovation so ethernet cable is run from our garage (from the switches) to each individual room through the walls.

In my room, my RJ45 drop connects to a NETGEAR switch which provides my desktop, xbox, TV (1 empty port) with connectivity.

The cable company technicians checked the quality of our co-axial cable signal and found that it was within normal operation specifications.

Can anyone suggest possible causes for cyclical lag like this? I am tech savvy but am absolutely stumped. I've exhausted every idea come up with, and even shelled out $100 for the new router hoping to solve our problems once and for all. Needless to say I am both sad and frustrated.

Thanks in advance
June 9, 2010 12:47:40 AM

Sorry to reply to my own post but I'd like to provide a preliminary update on the situation:

After brainstorming here for the past few hours, I decided to re-examine the network configuration and I noticed that the terminal that feeds the drop in my room was the only one connected to SMC Switch #2. I decided to bypass the switch and plug directly into LAN3 of the NETGEAR router and right now my pingplotter hammering www.google.com is showing consistent pings under 90ms (flat line on the graph).

If it is possible that a "switch" can go bad, then I may have just figured it out.

edit: Spoke to soon. Problem returned within 10-15 minutes after a full network reboot (after I bypassed the switch).
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June 17, 2010 6:06:08 PM

novaprospekt said:
Sorry to reply to my own post but I'd like to provide a preliminary update on the situation:

After brainstorming here for the past few hours, I decided to re-examine the network configuration and I noticed that the terminal that feeds the drop in my room was the only one connected to SMC Switch #2. I decided to bypass the switch and plug directly into LAN3 of the NETGEAR router and right now my pingplotter hammering www.google.com is showing consistent pings under 90ms (flat line on the graph).

If it is possible that a "switch" can go bad, then I may have just figured it out.

edit: Spoke to soon. Problem returned within 10-15 minutes after a full network reboot (after I bypassed the switch).


Funnily enough, I have the same problem with a WNR3500L. To verify I suggest you ping the router itself, and not your upstream provider. My WNR3500L serves my household with wireless connectivity and I see the same kind of cyclic ping issues (but mine are sometimes in the 10+s range).

The really sad part is that I bought this router to get better wireless coverage :)  Just like other household routers it's a piece of crap.
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June 18, 2010 9:25:11 PM

ecapitan said:
Funnily enough, I have the same problem with a WNR3500L. To verify I suggest you ping the router itself, and not your upstream provider. My WNR3500L serves my household with wireless connectivity and I see the same kind of cyclic ping issues (but mine are sometimes in the 10+s range).

The really sad part is that I bought this router to get better wireless coverage :)  Just like other household routers it's a piece of crap.


I don't use wireless though so I'm not sure if we have the same issue.

I actually ended up solving the problem after looking in the router's "status" seeing a bunch of external IP addresses appear to be DoS'ing one of my networked computers (querying an internal IP on the same or random port) multiple times a second (from random external IPs and ports).

I disabled and isolated the networked computer which was being attacked and the lag stopped. It either was P2P (Limewire) related, or virus/malware or both. But suffice to say, now every computer is cleaned up, no P2P either, and haven't had any more problems with this issue.

This was a completely -wired- issue though, can't stress that enough. I don't use wireless much because I do gaming.
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